Re: [PATCH] x86/acpi: fix suspend with Xen

From: Juergen Gross
Date: Tue Jan 17 2023 - 10:32:16 EST

On 17.01.23 15:09, Rafael J. Wysocki wrote:
On Mon, Jan 16, 2023 at 7:45 AM Juergen Gross <jgross@xxxxxxxx> wrote:

On 13.01.23 20:40, Rafael J. Wysocki wrote:
On Fri, Jan 13, 2023 at 3:06 PM Juergen Gross <jgross@xxxxxxxx> wrote:

Commit f1e525009493 ("x86/boot: Skip realmode init code when running as
Xen PV guest") missed one code path accessing real_mode_header, leading
to dereferencing NULL when suspending the system under Xen:

[ 348.284004] PM: suspend entry (deep)
[ 348.289532] Filesystems sync: 0.005 seconds
[ 348.291545] Freezing user space processes ... (elapsed 0.000 seconds) done.
[ 348.292457] OOM killer disabled.
[ 348.292462] Freezing remaining freezable tasks ... (elapsed 0.104 seconds) done.
[ 348.396612] printk: Suspending console(s) (use no_console_suspend to debug)
[ 348.749228] PM: suspend devices took 0.352 seconds
[ 348.769713] ACPI: EC: interrupt blocked
[ 348.816077] BUG: kernel NULL pointer dereference, address: 000000000000001c
[ 348.816080] #PF: supervisor read access in kernel mode
[ 348.816081] #PF: error_code(0x0000) - not-present page
[ 348.816083] PGD 0 P4D 0
[ 348.816086] Oops: 0000 [#1] PREEMPT SMP NOPTI
[ 348.816089] CPU: 0 PID: 6764 Comm: systemd-sleep Not tainted 6.1.3-1.fc32.qubes.x86_64 #1
[ 348.816092] Hardware name: Star Labs StarBook/StarBook, BIOS 8.01 07/03/2022
[ 348.816093] RIP: e030:acpi_get_wakeup_address+0xc/0x20

Fix that by adding an indirection for acpi_get_wakeup_address() which
Xen PV dom0 can use to return a dummy non-zero wakeup address (this
address won't ever be used, as the real suspend handling is done by the
hypervisor).

How exactly does this help?

I believed the first sentence of the commit message would make this
clear enough.

That was clear, but the fix part wasn't really.

I can expand the commit message to go more into detail if you think
this is really needed.

IMO calling acpi_set_waking_vector() with a known-invalid wakeup
vector address in dom0 is plain confusing.

I'm not sure what to do about it yet, but IMV something needs to be done.

Another possibility would be to modify acpi_sleep_prepare(), e.g. like the
attached patch (compile tested only).


Juergen
From 5a2de7250c4e8782ed89c7898061815058fa2710 Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@xxxxxxxx>
Date: Tue, 17 Jan 2023 16:20:04 +0100
Subject: [PATCH] acpi: fix suspend with Xen PV
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Commit f1e525009493 ("x86/boot: Skip realmode init code when running as
Xen PV guest") missed one code path accessing real_mode_header, leading
to dereferencing NULL when suspending the system under Xen:

[ 348.284004] PM: suspend entry (deep)
[ 348.289532] Filesystems sync: 0.005 seconds
[ 348.291545] Freezing user space processes ... (elapsed 0.000 seconds) done.
[ 348.292457] OOM killer disabled.
[ 348.292462] Freezing remaining freezable tasks ... (elapsed 0.104 seconds) done.
[ 348.396612] printk: Suspending console(s) (use no_console_suspend to debug)
[ 348.749228] PM: suspend devices took 0.352 seconds
[ 348.769713] ACPI: EC: interrupt blocked
[ 348.816077] BUG: kernel NULL pointer dereference, address: 000000000000001c
[ 348.816080] #PF: supervisor read access in kernel mode
[ 348.816081] #PF: error_code(0x0000) - not-present page
[ 348.816083] PGD 0 P4D 0
[ 348.816086] Oops: 0000 [#1] PREEMPT SMP NOPTI
[ 348.816089] CPU: 0 PID: 6764 Comm: systemd-sleep Not tainted 6.1.3-1.fc32.qubes.x86_64 #1
[ 348.816092] Hardware name: Star Labs StarBook/StarBook, BIOS 8.01 07/03/2022
[ 348.816093] RIP: e030:acpi_get_wakeup_address+0xc/0x20

Fix that by adding an optional acpi callback allowing to skip setting
the wakeup address, as in the Xen PV case this will be handled by the
hypervisor anyway.

Fixes: f1e525009493 ("x86/boot: Skip realmode init code when running as Xen PV guest")
Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
arch/x86/include/asm/acpi.h | 8 ++++++++
drivers/acpi/sleep.c | 6 +++++-
2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
index 65064d9f7fa6..8eb74cf386db 100644
--- a/arch/x86/include/asm/acpi.h
+++ b/arch/x86/include/asm/acpi.h
@@ -14,6 +14,7 @@
#include <asm/mmu.h>
#include <asm/mpspec.h>
#include <asm/x86_init.h>
+#include <asm/cpufeature.h>

#ifdef CONFIG_ACPI_APEI
# include <asm/pgtable_types.h>
@@ -63,6 +64,13 @@ extern int (*acpi_suspend_lowlevel)(void);
/* Physical address to resume after wakeup */
unsigned long acpi_get_wakeup_address(void);

+static inline bool acpi_skip_set_wakeup_address(void)
+{
+ return cpu_feature_enabled(X86_FEATURE_XENPV);
+}
+
+#define acpi_skip_set_wakeup_address acpi_skip_set_wakeup_address
+
/*
* Check if the CPU can handle C2 and deeper
*/
diff --git a/drivers/acpi/sleep.c b/drivers/acpi/sleep.c
index 0b557c0d405e..4ca667251272 100644
--- a/drivers/acpi/sleep.c
+++ b/drivers/acpi/sleep.c
@@ -60,13 +60,17 @@ static struct notifier_block tts_notifier = {
.priority = 0,
};

+#ifndef acpi_skip_set_wakeup_address
+#define acpi_skip_set_wakeup_address() false
+#endif
+
static int acpi_sleep_prepare(u32 acpi_state)
{
#ifdef CONFIG_ACPI_SLEEP
unsigned long acpi_wakeup_address;

/* do we have a wakeup address for S2 and S3? */
- if (acpi_state == ACPI_STATE_S3) {
+ if (acpi_state == ACPI_STATE_S3 && !acpi_skip_set_wakeup_address()) {
acpi_wakeup_address = acpi_get_wakeup_address();
if (!acpi_wakeup_address)
return -EFAULT;
--
2.35.3

Attachment: OpenPGP_0xB0DE9DD628BF132F.asc
Description: OpenPGP public key

Attachment: OpenPGP_signature
Description: OpenPGP digital signature